1. Field of the Invention
The present invention relates to a device for manufacturing an optical-fiber preform using a modified-chemical-vapor-deposition (MCVD) technique and, in particular, to a device for automatically leveling a silica tube while being subject to a traversing oxy-hydrogen heating.
2. Description of the Related Art
In general, the process of manufacturing an optical fiber is divided into two steps: the process of fabricating an optical-fiber perform, and the extrusion process of extruding a strand of optical fiber from the optical-fiber preform. Fabricating the core/inner cladding is well known in the art and can be performed in a variety of ways, such as the modified-chemical-vapor deposition (MCVD), which involves passing a high-purity gas through the interior of a silica tube while heating the outside of the tube wall.
FIG. 1 illustrates the conventional MCVD technique that is used to fabricate an optical preform. Two ends of the quartz tube T are fastened by a pair of chucks 12, each disposed in the opposite ends on a horizontal lathe 10, or the like. The quartz tube T is heated with a traversing burner B in the direction of an arrow A3, while being rotated in the direction of an arrow A1 of the A-axis. At the same time, oxygen gas with SiCl and other chemical substances is blown in the direction of an arrow A2 into the quartz tube T to form soot in the inner surface of the quartz tube T. In the heated area of the tube, a gas phase reaction occurs which deposits particles on the tube wall. The deposit is sintered as the heat passes over it. Once deposition is complete, the body is heated to collapse the tube and obtain a solid, consolidated preform in which the tube constitutes the outer portion of the inner cladding material.
During the process of manufacturing an optical-fiber preform as described above, it is necessary to conduct a routine check to ensure that the leveling state of the optical-fiber perform is substantially horizontal. This leveling process is often performed by a skilled operator to manually adjust the leveling of the optical-fiber perform to a desired point. To this end, the operator uses a leveling bar to adjust the horizontal orientation of the optical fiber preform using a polytetrafluoroethylene pad, wherein polytetrafluoroethylene is sold under the trademark teflon(trademark). As such, this type of leveling operation is susceptible to many human errors and requires a full-time person only dedicated to perform the leveling process. Accordingly, the leveling process currently being implemented is uneconomical and unreliable.
The present invention overcomes the above-described problems and provides additional advantages, by providing an automatic quartz-tube leveling device that is capable of automatically measuring the leveling state of an optical-fiber preform on a continuous basis, without requiring any additional operators to monitor the leveling state.
According to one aspect of the invention, an automatic quartz-tube leveling device for manufacturing an optical-fiber preform using a modified-chemical-vapor-deposition (MCVD) technique includes: a quartz tube disposed in a horizontal supporting element or its equivalent in order to manufacture the optical-fiber preform; a measuring device having at least one light-emitting device and at least one light-receiving device, the light-emitting device being disposed apart from the light-receiving device in an opposite position over the quartz tube, and for measuring an upper eccentric value and a lower eccentric value of an outer diameter along the length of the quartz tube; a controller for receiving the measured upper and lower eccentric values from the measuring device, for comparing the measured values with predetermined reference values to determine an eccentric difference amount, and for specifying a necessary leveling span to level the quartz tube to a desired point; and, a transfer device for adjusting the level of the quartz tube to the desired point based on the eccentric difference amount.
According to another aspect of the invention, a method for leveling a quartz tube when manufacturing an optical-fiber preform includes the steps of: providing the quartz tube in a substantially horizontal orientation; providing a traversing measuring device along the lateral direction of the quartz tube; measuring an upper eccentric value and a lower eccentric value with respect to an outer diameter of the quartz tube; comparing the measured upper and lower eccentric values with predetermined upper and lower reference values, respectively, to obtain an eccentric difference amount; and, simultaneously adjusting the leveling of the quartz tube according to the eccentric difference amount.
Preferably, the measuring device of the automatic quartz-tube leveling device includes a laser-scanning device.
Preferably, the measuring device includes a scanning area capable of radiation to an area larger than the longitudinal diameter of the quartz tube so as to measure the upper and lower eccentric values of the quartz tube. The scanning area is disposed directly facing the quartz tube.
Preferably, the transfer device further includes a control motor, a ball screw coupled with the control motor along a length of the quartz tube by using a coupler, a ball screw block coupled with the ball screw for movement along the length of the quartz tube according to revolutions of the control motor, and a leveling pad connectable to the ball screw block for carrying out a leveling operation for the quartz tube subsequently to movement to an instructed leveling span of the quartz tube by revolution of the ball screw.
Preferably, between the ball screw block and the leveling pad are further provided with a hydraulic or, more preferably, air cylinder and a spring. The spring may be connected between one arm of the hydraulic or air cylinder and the leveling pad.
Preferably, the leveling pad may consist of a polytetrafluoroethylene pad, wherein polytetrafluoroethylene is sold under the trademark teflon(trademark).